US 20100046219 A1
A light guide (11; 101; 111) comprising first and second oppositely arranged faces, an in-coupling portion (13 a-f) for in-coupling of light from a light-source (12 a-f; 95 a-f; 102; 106 a-c; 112 a-f), and an out-coupling portion (15 a-f; 103; 113 a-f) located adjacent to the in-coupling portion (13 a-f). The out-coupling portion (15 a-f; 103; 113 a-f) is configured to out-couple a primary light beam having a direction of propagation directed from a position in the in-coupling portion (13 a-f) with a lower out-coupling efficiency than a secondary light beam having a direction of propagation directed from a position in the light guide (11; 101; 111) outside the in-coupling portion (13 a-f). In this manner, a good mixing of light in the light guide can be achieved without imposing any particular requirements on the collimation of the in-coupled light.
1. A light guide comprising
first and second oppositely arranged faces;
an in-coupling portion for in-coupling of light from a light-source; and
an out-coupling portion located adjacent to said in-coupling portion, wherein
said out-coupling portion is configured to out-couple a primary light beam having a direction of propagation directed from a position in said in-coupling portion with a lower out-coupling efficiency than a secondary light beam having a direction of propagation directed from a position in the light guide outside said in-coupling portion;
said out-coupling portion comprises a plurality of out-coupling structures, and
said out-coupling structures include a plurality of grooves formed on at least one of said first and second faces of the light guide, each of said grooves essentially extending along a projection of a respective one of said primary light beams in said face of the light guide in said out-coupling portion.
2. The light guide according to
3. The light guide according to
4. The light guide according to
5. The light guide according to
6. The light guide according to
8. The light guide according to
10. The light guide according to
11. The light guide according to
12. The light guide according to
13. The light guide according to
14. A light output device comprising a light guide according to
15. A light-output device comprising a light-guide according to
16. The light-output device according to
The present invention relates to a planar light guide comprising first and second oppositely arranged faces, an in-coupling position for in-coupling of light from a light-source, and an out-coupling portion located adjacent to the in-coupling position.
The present invention further relates to a light-output device including such a light guide and at least one light-source.
As of today, fluorescent lighting is commonly used as the illumination system of choice for office lighting.
To enable architects and interior designers to create interior styles that clearly distinguish one building from the other, however, there is an increasing need to integrate lighting in interiors as unobtrusively as possible.
Conventional luminaires based on fluorescent lighting are known to have a minimum thickness of approximately 50 mm. Illumination systems based on alternative light-sources which allow for thin luminaries on the other hand, such as for illumination systems including a number of light-emitting diodes (LEDs) and a light guide for mixing and distributing the light emitted by the LEDs, offer much more freedom in designing the luminaire.
Achieving a sufficient degree of mixing of light in the light guide is an important factor for obtaining improved viewing characteristics for a luminaire based on the light guide. Such improvements may include, for example, increased uniformity of the light out-coupled from the light guide, and reduced maximum brightness.
WO 2006/034831 discloses one approach for achieving such mixing, according to which the light guide is provided with pyramid-shaped out-coupling facets which form such an angle with the out-coupling face that nearly parallel light undergoes several reflections in the light guide before being out-coupled.
A drawback of the light guide described in WO 2006/034831 is that it requires in-coupled light to be highly collimated to function properly.
It is therefore an object of the present invention to mitigate at least some of the drawbacks of the prior art and to provide an improved light guide, enabling use of a wider variety of light-sources.
According to the present invention, these and other objects are achieved by a light guide comprising first and second oppositely arranged faces, an in-coupling portion for in-coupling of light from a light-source, and an out-coupling portion located adjacent to the in-coupling portion. The out-coupling portion is configured to out-couple primary light beams having a direction of propagation directed from a position in the in-coupling portion with a lower out-coupling efficiency than a secondary light beam having a direction of propagation directed from a position in the light guide outside the in-coupling portion.
The light-guide may, for example, be made of a slab of a single dielectric material or combinations of dielectric materials. Suitable dielectric materials include different transparent materials, such as various types of glass, poly-methyl methacrylate (PMMA) etc. The light guide may be planar, flat or have a curved appearance. A slab-type light guide typically relies upon total internal reflection (TIR) in order to contain light coupled into the waveguide.
In a particular out-coupling portion of the light guide, a secondary light beam may originate from another in-coupling portion which may be comprised in the light guide, or may be light which originally comes from the in-coupling portion associated with the particular out-coupling portion, but has changed it direction of propagation due to, for example, reflection.
It should be noted that a light beam which is a primary light beam in one out-coupling portion is typically a secondary light beam in another out-coupling portion associated with another in-coupling portion, if any.
By configuring the out-coupling portion such that it out-couples primary light beams with a lower out-coupling efficiency than secondary light beams, it is ensured that a significant portion of the in-coupled light undergoes a number of reflections in the opposite faces of the light guide before being out-coupled as secondary light. This may, for example, be achieved by configuring the out-coupling portion such that the TIR (total internal reflection) condition is fulfilled for primary light beams, but not for secondary light beams.
In this manner, a good mixing of light in the light guide can be achieved without imposing any particular requirements on the collimation of the in-coupled light.
The light guide according to the invention may further comprise redirection means for redirecting the primary light beam, thereby converting the primary light beam into a secondary light beam.
Such a redirection means may comprise active and/or passive means. Active means may, for example, include an optical element having a controllable refractive index and/or reflectance, and passive means may, for example, include a fixed reflective structure and/or an interface between materials having different refractive indices.
The primary light beam propagating in a direction of propagation directed from the in-coupling portion can for instance be reflected by one or several reflectors which may be positioned at an edge of the light guide, or at a boundary of segments of the light guide. The reflectors at such segment boundaries may, for example, be formed by air gaps or another substance having a low refractive index, by a semi-transparent reflector coating or through selective provision of an essentially completely reflective coating. Such segments may be light guides which are assembled to form a composite light guide, or a light guide can be partly separated into segments by, for example, forming slits partly extending through the light guide at appropriate locations.
When, following reflection at the reflective structure, a light beam originally being directed from an in-coupling portion travels through the out-coupling portion in a different direction, it is more likely to be out-coupled. Thus, improved uniformity is obtained, even for light guides having a single in-coupling portion. Consequently, the provision of redirecting means improves the spatial as well as the angular mixing of light-beams in the light guide. This may be especially advantageous in situations where a plurality of differently colored light-sources are used in the light-guide.
The light guide according to the invention can further comprise an in-coupling structure formed at the in-coupling portion.
Such an in-coupling structure is a structure which is adapted to enable in-coupling of light from a light-source into the light guide, and can be arranged in various locations, such as at an edge of the light guide, somewhere along one of the oppositely arranged faces of the light guide, or internal to the light guide.
Moreover, the in-coupling structure may comprise beam-shaping means for collimating the in-coupled light.
By collimating light should here be understood limiting the angular distribution of light emitted by a light-source.
Through the provision of such beam-shaping means, in combination with a properly designed light-guide, collimated light can be out-coupled from the light-guide. This is important for, in particular, office lighting where glare should be avoided or at least limited.
The beam-shaping means may comprise conventional collimating optical elements, such as, for instance, reflective funnels or TIR elements. Alternatively, or in combination with such optical elements, the beam shaping means may be provided through a suitable geometry of the in-coupling structure itself.
The in-coupling structure may, furthermore, comprise a recess formed in the light guide from the first or second face.
The recess may extend partly through the light guide, or be formed as a through-going hole.
Hereby, a light-source can conveniently be inserted into the light guide from any of its faces.
For a light-guide having multiple in-coupling portions, these may advantageously be formed as recesses distributed over one of or both faces, enabling a uniform distribution of light-sources across the light guide.
Furthermore, the recess may advantageously have a rectangular cross-section in a plane parallel to the light guide, thereby enabling collimation of in-coupled light in a plane parallel with the light guide.
An in-coupling recess having a rectangular cross-section enables splitting of light emitted by a light-source emitting light in all directions, such as for instance an omni-directional LED, into separate beams along two orthogonal axes in a plane parallel with the light guide.
Such a recess configuration consequently limits the directions of primary light beams in a plane parallel with the light guide. This in turn facilitates the manufacture of the light guide, in particular with respect to the out-coupling portion.
Moreover, the light-guide according to the present invention may advantageously further comprise a collimating layer for decreasing angular spread of light out-coupled by the out-coupling portion.
By “collimating layer” should be understood a layer that collimates, that is, decreases the angular spread of light passing therethrough.
Through the provision of a collimating layer, the amount of glare can be reduced, which is especially advantageous when the light-guide is used in a luminaire for general lighting purposes.
The collimating layer may be provided on either face of the light-guide and may comprise any kind of collimating optical element known to the skilled person. For example, the collimating layer may comprise spaced apart structures with essentially triangular cross-sections, such that a funnel-like collimating structure is formed. Alternatively, a so-called concentric parabolic concentrator (CPC) can be used to further improved the collimation.
Collimating structures, whether having the above-mentioned triangular cross-section or any other collimating shape, such as the above mentioned CPC, may, for example be manufactured using extrusion moulding and subsequently applying a reflective coating to the structures. The coating may advantageously be applied on all sides of the collimating structures, but especially when there is no optical contact between the light-guide and the collimating structures, the reflecting coating on the side of the structures facing the light-guide can be dispensed with.
Additionally, the out-coupling portion may comprise a plurality of out-coupling structures.
These out-coupling structures may be provided on either of the faces of the light guide or internal to the light guide, and may be any structure exhibiting a direction dependent out-coupling performance. As an alternative or combination to the provision of out-coupling structures, the direction dependent out-coupling can be realized by means of, for example, suitable spatial variations in the refractive index of the light guide.
These out-coupling structures may advantageously include a plurality of grooves formed on at least one of the first and second faces of the light guide, each of the grooves essentially extending along a projection of a respective one of the primary light beams in the face of the light guide.
Forming out-coupling grooves, which run parallel to the main direction of the light directed from the in-coupling portion, on at least one of the faces, ensures that the light travels a certain distance, and is hence spread over a certain area, before it is coupled out. The light may, following reflection, be out-coupled in the out-coupling portion associated with the light-source from which it originated, or be out-coupled in a neighboring out-coupling portion.
The grooves can for instance be V-shaped, and have sides, or facets, which may advantageously be provided with a reflective coating.
According to one exemplary, collimation conserving configuration, the grooves may have an essentially V-shaped cross-section, with an opening angle of approximately 90°.
As an alternative or a complement to such a collimation conserving groove configuration, the light-guide may be provided with a collimating layer that comprises collimating structures which are aligned with the out-coupling structures. For out-coupling structures provided in the form of grooves, the collimating structures may then run in parallel with the grooves to collimate the light that is out-coupled by the grooves.
Through the provision of such collimating structures aligned with the out-coupling structures, a sufficiently low level of glare can be achieved without making the out-coupling structures as such collimation conserving. Hence, a larger variety of out-coupling structures can be used, which may facilitate manufacturing and thus lead to a reduced cost of the light-guide.
For optimal performance of the collimating structures, they should be well aligned with the out-coupling structures. Preferably, lateral misalignment between the collimating structures and substantially parallel out-coupling structures should be below 10% of the distance between neighboring out-coupling structures (the out-coupling structure pitch). Moreover, the angular displacement (rotation relative to the out-coupling structures) (in radians) of the collimating structures should preferably be smaller than 10% of the ratio between the distance between neighboring out-coupling structures and the length of the light-guide.
According to one embodiment, the out-coupling portion may, furthermore, include a portion of the light guide having an increasing thickness with increasing distance from the in-coupling portion.
By providing such an outwardly flaring structure with respect to the in-coupling portion, the angle of incidence on a face of the light guide of a light-beam having a given direction in a plane perpendicular to the light guide becomes dependent on the direction of the light beam in the plane of the light guide. A primary light beam which is directed from the in-coupling portion will be out-coupled with a lower out-coupling efficiency than a secondary light beam having another direction.
This structure may be provided as an alternative to, or in combination with the above-mentioned grooves.
In order to achieve a highly efficient out-coupling of light from the light-guide, the light-guide may additionally include a reflective layer arranged on one side thereof.
When the out-coupling portion comprises out-coupling structures at one face of the light-guide, the reflective layer may be provided on the same or opposite face depending on the configuration of the out-coupling structures.
In case the out-coupling structures are grooves, the reflective layer may be provided on some or all of the facets of the grooves. Alternatively, the reflective layer may be provided in the form of a reflective film that is arranged essentially in parallel with the light-guide at the out-coupling portion thereof.
By using such a reflective layer instead of applying a reflective layer on the facets of the grooves, manufacturing of the light-guide may be facilitated, however, typically at the cost of a decreased degree of collimation of the out-coupled light.
Such a reflective film may therefore advantageously be used in combination with the above-mentioned collimating layer.
Advantageously, optical contact between such a reflective film and the light-guide may substantially be prevented to avoid loss of light caused by unnecessary reflections in the reflective film. It is therefore preferred that essentially only light that is out-coupled from the light-guide by the out-coupling portion thereof hits the reflective film.
Optical contact can be prevented by spacing the reflective film apart from the light-guide. It should, furthermore, be noted that if a reflective film is placed in mechanical contact with a light-guide, there is typically hardly any optical contact therebetween.
Advantageously, the light guide according to the present invention can comprise a plurality of in-coupling portions, each being adapted to in-couple light from an associated light-source, and a plurality of out-coupling portions, each being adjacent to a corresponding one of the in-coupling portions and configured to out-couple a primary light beam having a direction of propagation directed from a position in the corresponding in-coupling portion with a lower out-coupling efficiency than a secondary light beam a direction of propagation directed from a position in the light guide outside the corresponding in-coupling portion.
In order to obtain suitable office as well as home illumination, it is desirable that light emitted from a light guide is uniformly distributed and that an uncomfortably high maximum local brightness is avoided. Uniform distribution of light can be obtained by having light emanating from a plurality of light-sources. However, light-sources, such as light-emitting diodes (LEDs), typically have slightly different color and flux characteristics, known as the binning problem. Thus, the light emitted by the different light-sources should preferably be well mixed in the light guide before being out-coupled in order to achieve a uniform distribution of out-coupled light. A good mixing of light is obtained, as primary beams to a large extent are contained within the light guide such that they travel a certain distance, and hence are spread over a certain area, before being coupled out as secondary light beams.
Light from a plurality of in-coupling portions, mixing in the light guide, furthermore contributes to robustness against failure of a few of the light-sources.
The light guide may, furthermore, advantageously comprise at least one guiding portion located between neighboring out-coupling portions to prevent cross-talk therebetween.
For some types of out-coupling structures, such as grooves with reflective sides, which may be provided on one or both faces of the light guide, a light beam may be out-coupled through successive reflections in sides of two or more grooves. Such successive reflections, which would typically result in an unwanted redirection of the out-coupled light beam, can be avoided by providing an unstructured guiding portion at least between selected portions of neighboring out-coupling portions.
Furthermore, the in-coupling portions can be arranged in an array forming a rectangular grid pattern.
The grid pattern may be formed by square or non-square rectangles.
Additionally, the light guide according to the invention may further comprise at least one omni-directional out-coupling portion configured to out-couple light beams with essentially equal out-coupling efficiency regardless of their direction in a plane parallel with the light guide.
By providing such omni-directional out-coupling structures at suitable locations across the light guide, preferably between out-coupling portions associated with neighboring in-coupling portions, it is ensured that light-beams originating from one in-coupling portion which happen to have a direction coinciding (or being diametrically opposite) with that of a primary light beam in an out-coupling portion associated with another in-coupling portion is in fact out-coupled from the light-guide and does not proceed to be absorbed or scattered at an in-coupling portion.
The omni-directional out-coupling structures may be provided in the form of any conventional out-coupling structures which out-couple light independent of the direction, in the plane of the light-guide, of the light.
Furthermore, the light guide according to the invention can comprise a plurality of omni-directional out-coupling portions, each being located on a diagonal in the rectangular grid pattern array, between two neighboring in-coupling portions.
Moreover, the planar light guide having a plurality of in-coupling portions arranged in a grid-shaped array may advantageously comprise a plurality of in-coupling recesses, each being provided at a corresponding one of the in-coupling portions and having a rectangular cross-section parallel to the planar light guide, wherein opposite corners of each of the rectangular in-coupling recesses essentially coincides with a corresponding grid line in the grid pattern, and each of the out-coupling portions comprises four sets of grooves being essentially parallel within each set, provided on at least one of the first or second faces, each set of grooves extending substantially perpendicularly to an associated side of the rectangular in-coupling recess.
In this configuration, the rectangular in-coupling structures collimate the light, enabling the provision of simplified out-coupling structures extending in two principal directions only.
As stated above, the in-coupling recesses may be provided in a square or a non-square grid-shaped array. By selecting a non-square grid, the out-coupling grooves are not directed directly at a neighboring in-coupling structure. Hereby, less light is lost by absorption or scattering at neighboring in-coupling positions.
The light guide according to the present invention can furthermore advantageously be comprised in a light output device, such as a luminaire, further comprising at least one light-source arranged at said in-coupling portion.
Other aspects, benefits and advantageous features of the present invention will be apparent from the following description and claims.
These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing a currently preferred embodiment of the invention, wherein:
The present detailed description primarily relates to luminaires comprising a planar light-guide and one or several light-emitting diodes arranged in in-coupling recesses provided in one of the faces of the light-guide.
It should be noted that this by no means limits the scope of the invention, which is equally applicable to other types of light-sources, such as semiconductor lasers, and other kinds of in-coupling structures, including, for examples mirrors, prisms etc.
In the following, a number of preferred embodiments will be described.
First, with reference to
By forming the in-coupling structure as a recess 14 having a rectangular/square cross-section in the plane of the light guide 11, light emitted by an uncollimated light-source 12 e, such as an omni-directional LED, is collimated in the plane of the light guide 11 and thus split into four separate beams 18 a-d along two orthogonal axes as schematically indicated in
As can be seen in
The out-coupling of light emitted by a particular light-source need not necessarily take place in an out-coupling portion of the light guide associated with another light-source, as is illustrated in
This effect may be achieved in a variety of ways. For example, the light guide 11 may comprise separate light guides which may, for example, coincide with the out-coupling portions referred to above. These separate light guides may, for example, be isolated from each other by air slits.
As is schematically illustrated in FIG. Ic, the light distribution across the luminaire is then completely altered, due to reflections at the boundaries between the light guide segments. As an alternative to the air slits 23 a-b indicated in FIG. Ic, the light guide segments may be glued together with a low refractive-index glue, in which case the respective fractions of light reflected at segment boundaries and crossing segment boundaries will shift, leading to a distribution of out-coupled light which is intermediate between the situations illustrated in
The redirection discussed above in connection with
In the luminaire 10 in
The reason for these colored bands to appear is that when looking at certain positions into the luminaire 10 only certain light-sources are visible that each seem to be at a different location.
Through the provision of the semitransparent mirror 25 at the boundaries between the out-coupling portions, as indicated in
To achieve an even further improved color mixing, however, also the special conditions at the edges of the luminaire should be considered.
This is schematically illustrated in
Furthermore, an essentially completely reflective mirror 26 should be present along the outer boundary of the luminaire 10. As an alternative to half sized and quarter sized light-sources, full-size light-sources with half and quarter intensity may be used. When the light-sources 28 a-b, 29 a-j are realized using light-emitting diodes (LEDs), one option is to provide each of the light-sources 28 a-b located in the interior in the form of 4 LEDs, and provide the light-sources along the boundary in the form of 2 LEDs and one LED, respectively. In this case, each of the LEDs should emit substantially the same amount of light.
The semitransparent mirrors 25 between the out-coupling portions 15 a-f in
Furthermore, the luminaires shown in
It should be noted that the luminaire 10 described above, as well as other exemplary luminaires discussed below are illustrated in a simplified and schematic manner. In particular, a real luminaire typically has a considerably larger number of light-sources. However, the embodiments disclosed herein should be sufficient for enabling a person skilled in the relevant art to make and use the present invention. With reference to
Turning now to
Simulations and experiments have shown that an improved collimation in the plane of the light-guide can be achieved by making the walls 30 a-d of the recess 14 concave as is schematically illustrated in
With reference to
Having thus described various in-coupling structure configurations in connection with
As is evident from
Through a suitable configuration of such V-shaped out-coupling grooves 21 as schematically illustrated in
As is schematically illustrated in
As mentioned above, glare perceived by a user of the luminaire 10 can be reduced by providing out-coupling structures that conserve the collimation of the light in the light-guide 11. An example of such collimation-conserving out-coupling structures are the grooves 21 with reflecting sides or facets 44 a-b shown in
A comparison between such a configuration with out-coupling grooves 21 having reflective facets 44 a-b and configurations without reflective facets will now be made with reference to
In each of
In the luminaire portion schematically shown in
The exemplary collimating layer 53 shown in
The collimating layer 53 may be provided in the form of separate rods 54 a-b, or as a sheet comprising a plurality of rods. For example, adjacent rods may be joined by perpendicularly extending rods.
To demonstrate the collimation conserving properties of the various configurations illustrated in
length of outcoupling portion 15 a: 72 mm;
width of outcoupling portion 15 a: 48 mm;
light-guide 11 thickness: 4 mm;
pitch of the V-grooves 21: 4 mm;
width of the grooves 21: 1 mm;
depth of the grooves: 0.5 mm;
distance between rods 54 a-b at base: 2 mm
pitch of rods: 4 mm;
height of rods: 4 mm;
pincushion shaped in-coupling recesses with length of sides: 8.5 mm
radius of curvature of sides: 8 mm; and
light-sources: side-emitting LEDs.
As can be seen from the radial plot 60 for the configuration of
When simply replacing the reflective coating on the facets 45 a-b of the grooves 21 by a reflective film 52 without also adding a collimating layer, there is considerable intensity also at larger angles as is illustrated by the radial plot 61.
As is evident from the last plot 62 in
One way of improving the angular non-uniformity resulting from this effect is schematically illustrated in
Another way of improving the above-discussed angular non-uniformity resulting from absorption of light at neighboring in-coupling portions is schematically illustrated in
These omni-directional out-coupling structures are capable of out-coupling light traveling in any one of the principal directions (45°, 135°, 225°, 315° according to the notation used in the description relating to
In addition to the above-described exemplary embodiments of the present invention, a large number of variations are possible and may, depending on area of application, be advantageous to use.
In the embodiments described so far, the situation with light being in-coupled into the light guide in four main directions with a certain beam width has been described. Obviously, the light-source(s) and/or the in-coupling structures may alternatively be configured in such a way that light is in-coupled in fewer principal directions. Hereby, the interaction between neighboring in-coupling portions may be reduced or even completely eliminated. An exemplary luminaire utilizing light in-coupled in two principal directions only is schematically illustrated in
The unused in-coupling facets 97 a-b may be provided with a reflector or an out-coupling facet, in order to reduce interactions between neighboring light-sources.
As will be described below with reference to
As a result thereof, practically no light will be out-coupled before reflection at the reflective edges 104 a-d of the light guide 101. By suitably tuning the out-coupling structures 103 with respect to their distance from the reflecting edges 104 a-d and the overall geometry of the light-guide 101, a uniform output of light across the lighting device 100 can be achieved with the single light-source 102.
The uniformity of the out-coupled light may be improved further by using diffusively reflecting edges 104 a-d. However, this may increase the angular distribution of the out-coupled light.
The groove-shaped out-coupling structures implemented in the embodiments described above is only one example of direction dependent out-coupling structures which may be comprised in the light guide according to the present invention.
An additional exemplary out-coupling structure, which can be implemented as an alternative to or in combination with the previously described V-shaped grooves, will now be described with reference to
The direction dependent out-coupling of these out-coupling structures 114 a-d will now be described with reference to
The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments. For example, out-coupling grooves having transparent sides on the emitting face of the light guide may be provided instead of, or in combination with the grooves with reflective sides described above. Furthermore, the out-coupling structures may be provided as grooves that extend in a radial direction from each in-coupling portion. Moreover, many other in-coupling configurations are feasible, including recesses or holes having a cylindrical cross-section in the plane of the light guide.